In order to ensure power semiconductors are cooled, the semiconductors are placed in thermally conductive contact with a heat sink. In cost-effective embodiments, this is usually realized with springs which press the semiconductor component against the heat sink.
An arrangement of this type is described in German utility model G 92 13 671.0. By virtue of a retaining spring element being pre-mounted in a housing part, the components to be cooled are pressed against an inner wall of the heat sink by spring tongues of the retaining spring when the housing parts are subsequently assembled.
In a similar way, U.S. Pat. No. 5,274,193, German laid-open specification 36 12 862 A1, German patent specification 195 43 260 C2 and German utility model DE 200 14 739 U1 describe spring elements which are clamped between power semiconductors and a housing. The difference in each case is the way in which the spring elements are supported on or fixed to the housing. For example, the spring element may be retained itself by recesses and webs of the housing or by means of additional fixing elements such as screws or clamping rails.
Some retaining apparatuses have a substantially U- or L-shaped spring clip that is placed (“clipped”) over a heat sink wall and at the same time over the component and in this way ensures the contact-pressure force between the bearing faces of the heat sink and of the component.
In all apparatuses without additional fixing elements, such as German utility model G 92 13 671.0, the problem arises of the component and the solder point being subjected to shear stresses. This can lead to damage to the component or the solder connection. The shear stresses are produced by forces which act on the component when the apparatus is assembled in a plane parallel to the cooling system surface of the components or the heat sink. Therefore, for example in G 92 13 671.0, the upper housing part is placed on the lower housing part from above by way of a snap-in retaining spring and in the process, the spring is guided along the perpendicular component, as a result of which a force acts in the direction of or in the opposite direction to the connection wires. The spring element may also be likewise inserted parallel to the bearing face of the component as per DE 195 43 260 C2 by means of being pressed in the opposite direction to the connection wires. Although in U.S. Pat. No. 5,274,193, no shear force acts on the components, the retaining spring has to be fixed and the retaining force of the spring element has to be generated by an additional clamping rail.